Large amounts of waste heat of varying temperature are produced in Sweden and in the rest of the world. This heat is often disposed of to the surroundings, for example to lakes, watercourses, etc. Vast economical and environmental advantages can be reached if this waste heat can be refined. Around the world there is industries that is in need of large amounts of heat at high temperature and that produces large amounts of waste heat at lower temperatures. In Sweden there is example of utilization of waste heat for heating purposes, for example to the district heating net-work, from processes that requires a great deal of energy. Depending on the waste heat temperature, there can be some limitations in the utilization, such as temperature demand on the district heating network, distance between waste heat and the district heating network, etc. However, sometimes the waste heat surplus cannot be used at all for heating purposes, depending on the time of the year or that there is no addressee of the heat.
EP-A2-1174590 discloses a method and an apparatus for production of electricity, where a liquid such as water is evaporated in a first system and transfer heat through an evaporator to a cooling agent that circulates in a second system, separated from the first system, where the cooling agent expands and produces electricity. The evaporation occurs at a relatively high temperature, about 200° C.